Enzyme-catalyzed reactions have the advantages of proceeding with great chemical specificity under relatively mild conditions, and often accomplish what man finds difficult, if not impossible, to duplicate in the laboratory. For such reasons there is increasing emphasis on the use of enzymatic processes on a commercial scale. One example, of many which could be cited, is the conversion of glucose to fructose using glucose isomerase.
Enzymes often are water soluble, and if they are merely used in aqueous solutions recovery of enzymes for reuse is difficult and expensive. Using the enzyme only once affords a process which is relatively expensive. Consequently, many techniques have been developed for immobilizing the enzyme in such a way that substantial enzymatic activity is displayed while the enzyme itself remains rigidly attached to some water-insoluble support, thereby permitting reuse of the enzyme over substantial periods of time and for substantial amounts of feedstock. One illustration of a method for immobilizing an enzyme is found in U.S. Pat. No. 4,141,857, where a polyamine is absorbed on a metal oxide such as alumina, treated with an excess of a bifunctional reagent, such as glutaraldehyde, so as to cross-link the amine, and then contacting the mass with enzyme to form covalent bonds between the pendant aldehyde groups and an amino group on the enzyme. The support matrix prepared according to the aforementioned invention has great utility in immobilizing reactive chemical entities, enzymes being but one class of such reactive chemical entities.
An immobilized enzyme system is the material which results from immobilization of an enzyme onto a support matrix. Magnetic support matrices and immobilized enzyme systems offer several advantages when compared to non-magnetic systems. For example, separation of such materials from other non-magnetic solids by use of a magnetic field can permit separations otherwise difficult or impossible to perform. Such a situation is represented by the case where two enzymes, with different deactivation times, are used concurrently on a substrate, with one immobilized enzyme system magnetic and the other non-magnetic. In this case, after one enzyme is exhausted, the other may be readily recovered and reused by magnetic separation of the two immobilized enzyme systems, which will be recognized as offering great benefits in economy. Another advantage of such magnetic materials is their use in a magnetically stabilized fluid bed, thereby presenting further options in continuous reactor systems.
U.S. Pat. No. 4,152,210 describes a support matrix comprised of particulates of ferromagnetic materials. Enzymes are bound thereto by reagents which react with a film of metal oxide on the surface of the particulates, or to polymeric material attached to the support. A serious disadvantage of such a support matrix is its high density. This disadvantage is overcome in U.S. Pat. No. 4,177,253 which describes a ferromagnetic composite comprising a low density core whose surface is coated with magnetic materials. Because more than 50% of the surface must be so coated, the latter support matrix presents the disadvantage of reducing the number of sites available for subsequent enzyme bonding, thus presenting substantial limitations on the amount of enzyme which can be immobilized. Additionally, because a surface coating of ferromagnetic material necessitates a method of preparation which is reasonably elaborate, complex, and demanding, such supports can be expected to be reasonably expensive and commercially unfeasible. Magnetic supports for immobilized enzymes and bioaffinity adsorbents has been reviewed by Halling and Dunnill, Enzyme Microb. Technol., 2, 2-10 (1980).
It is highly desirable to have a magnetic support matrix whose only difference from a conventional one is its magnetic properties, and which can be readily prepared by simple procedures. In part this dictates a magnetic support whose ferromagnetic materials are not bound as a surface coating and which may be prepared by a variation in the basic method of preparation.